Storage devices write data or the like to a recording medium using an actuator arm with a head provided to the tip of the actuator arm. The recording medium has data areas to store user data and servo areas to store data used for positioning control of the head.
In such a storage device, when the head passes over a servo area, the position of the head is determined based on a signal read out from the servo area. The arm adjusts the head position based on the position determined. Thus, the head can be controlled to be located at a desired position.
There are several types of patterns recorded in the servo areas including, for example, null servo patterns, area servo patterns, and phase servo patterns. The use of these servo patterns recorded in the servo areas allows determining the position of the head.
However, in a storage device, it is difficult to determine the position of the head simply based on positional information read out from a servo pattern. This is because it is difficult to associate the signal read out with the position of the head in a smooth correspondence relation due to moving of the head, for example. Therefore, in a storage device, a correction process is required for the signal read out to determine the position of the head more accurately.